1. Field of the Invention
The present invention relates to a zoom lens and an image-pickup apparatus having the zoom lens.
2. Description of the Related Art
One conventional small and high magnification varying zoom lens is a zoom lens including a lens unit having a positive refractive power arranged closest to the object side. For example, Japanese Patent Laid-Open No. (“JP”) 2009-3342 proposes a four-unit zoom lens in which positive, negative, positive and positive units are arranged in order from the object side. JP 2009-164847 discloses an image-pickup apparatus configured to realize electronic zooming with optical zooming and to enable an object image to be observed at a high zooming ratio.
In most of zoom lenses including the lens unit having the positive refractive power arranged closest to the object side, as disclosed in JP 2009-3342, a front lens diameter is determined by an off-axis ray at a position (intermediate focal length) located on the optical axis of the zoom lens, except the wide-angle end and a telephoto end. Usually, a range of an image-pickup element available at the intermediate focal length is utilized from the wide-angle end to the telephoto end.
For a wide working range of the image-pickup element with a small front lens diameter, a minimum necessary light amount at the intermediate focal length is effective, but even this configuration cannot maintain small a front lens diameter in a wide-angle zoom lens. Although JP 2009-3342 provides four lenses to the first lens unit and restrains a large size of a front lens diameter caused by the wide-angle configuration, this configuration is insufficient for the reduced front lens diameter. The conventional electronic zooming, as disclosed in JP 2009-164847, does not limit the zoom lens in the image-pickup apparatus or is silent about a means for reducing the front lens diameter of the wide-angle zoom lens.